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From: John Fastabend <john.fastabend@gmail.com>
To: Lorenz Bauer <lmb@cloudflare.com>,
	jakub@cloudflare.com, john.fastabend@gmail.com,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Lorenz Bauer <lmb@cloudflare.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>
Cc: kernel-team@cloudflare.com, netdev@vger.kernel.org,
	bpf@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: RE: [PATCH bpf-next 5/6] bpf: sockmap: allow update from BPF
Date: Wed, 19 Aug 2020 14:22:55 -0700	[thread overview]
Message-ID: <5f3d982f51f22_2c9b2adeefb585bccb@john-XPS-13-9370.notmuch> (raw)
In-Reply-To: <20200819092436.58232-6-lmb@cloudflare.com>

Lorenz Bauer wrote:
> Allow calling bpf_map_update_elem on sockmap and sockhash from a BPF
> context. The synchronization required for this is a bit fiddly: we
> need to prevent the socket from changing it's state while we add it
> to the sockmap, since we rely on getting a callback via
> sk_prot->unhash. However, we can't just lock_sock like in
> sock_map_sk_acquire because that might sleep. So instead we disable
> softirq processing and use bh_lock_sock to prevent further
> modification.
> 
> Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
> ---
>  kernel/bpf/verifier.c |  6 ++++--
>  net/core/sock_map.c   | 24 ++++++++++++++++++++++++
>  2 files changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 47f9b94bb9d4..421fccf18dea 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -4254,7 +4254,8 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
>  		    func_id != BPF_FUNC_map_delete_elem &&
>  		    func_id != BPF_FUNC_msg_redirect_map &&
>  		    func_id != BPF_FUNC_sk_select_reuseport &&
> -		    func_id != BPF_FUNC_map_lookup_elem)
> +		    func_id != BPF_FUNC_map_lookup_elem &&
> +		    func_id != BPF_FUNC_map_update_elem)
>  			goto error;
>  		break;
>  	case BPF_MAP_TYPE_SOCKHASH:
> @@ -4263,7 +4264,8 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
>  		    func_id != BPF_FUNC_map_delete_elem &&
>  		    func_id != BPF_FUNC_msg_redirect_hash &&
>  		    func_id != BPF_FUNC_sk_select_reuseport &&
> -		    func_id != BPF_FUNC_map_lookup_elem)
> +		    func_id != BPF_FUNC_map_lookup_elem &&
> +		    func_id != BPF_FUNC_map_update_elem)

I lost track of a detail here, map_lookup_elem should return
PTR_TO_MAP_VALUE_OR_NULL but if we want to feed that back into
the map_update_elem() we need to return PTR_TO_SOCKET_OR_NULL
and then presumably have a null check to get a PTR_TO_SOCKET
type as expect.

Can we use the same logic for expected arg (previous patch) on the
ret_type. Or did I miss it:/ Need some coffee I guess.

>  			goto error;
>  		break;
>  	case BPF_MAP_TYPE_REUSEPORT_SOCKARRAY:
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index 018367fb889f..b2c886c34566 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -603,6 +603,28 @@ int sock_map_update_elem_sys(struct bpf_map *map, void *key,
>  	return ret;
>  }
>  
> +static int sock_map_update_elem(struct bpf_map *map, void *key,
> +				void *value, u64 flags)
> +{
> +	struct sock *sk = (struct sock *)value;
> +	int ret;
> +
> +	if (!sock_map_sk_is_suitable(sk))
> +		return -EOPNOTSUPP;
> +
> +	local_bh_disable();
> +	bh_lock_sock(sk);

How do ensure we are not being called from some context which
already has the bh_lock_sock() held? It seems we can call map_update_elem()
from any context, kprobes, tc, xdp, etc.?

> +	if (!sock_map_sk_state_allowed(sk))
> +		ret = -EOPNOTSUPP;
> +	else if (map->map_type == BPF_MAP_TYPE_SOCKMAP)
> +		ret = sock_map_update_common(map, *(u32 *)key, sk, flags);
> +	else
> +		ret = sock_hash_update_common(map, key, sk, flags);
> +	bh_unlock_sock(sk);
> +	local_bh_enable();
> +	return ret;
> +}
> +
>  BPF_CALL_4(bpf_sock_map_update, struct bpf_sock_ops_kern *, sops,
>  	   struct bpf_map *, map, void *, key, u64, flags)
>  {
> @@ -687,6 +709,7 @@ const struct bpf_map_ops sock_map_ops = {
>  	.map_free		= sock_map_free,
>  	.map_get_next_key	= sock_map_get_next_key,
>  	.map_lookup_elem_sys_only = sock_map_lookup_sys,
> +	.map_update_elem	= sock_map_update_elem,
>  	.map_delete_elem	= sock_map_delete_elem,
>  	.map_lookup_elem	= sock_map_lookup,
>  	.map_release_uref	= sock_map_release_progs,
> @@ -1180,6 +1203,7 @@ const struct bpf_map_ops sock_hash_ops = {
>  	.map_alloc		= sock_hash_alloc,
>  	.map_free		= sock_hash_free,
>  	.map_get_next_key	= sock_hash_get_next_key,
> +	.map_update_elem	= sock_map_update_elem,
>  	.map_delete_elem	= sock_hash_delete_elem,
>  	.map_lookup_elem	= sock_hash_lookup,
>  	.map_lookup_elem_sys_only = sock_hash_lookup_sys,
> -- 
> 2.25.1
> 



  parent reply	other threads:[~2020-08-19 21:23 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-19  9:24 [PATCH bpf-next 0/6] Allow updating sockmap / sockhash " Lorenz Bauer
2020-08-19  9:24 ` [PATCH bpf-next 1/6] net: sk_msg: simplify sk_psock initialization Lorenz Bauer
2020-08-19 20:05   ` John Fastabend
2020-08-19  9:24 ` [PATCH bpf-next 2/6] bpf: sockmap: merge sockmap and sockhash update functions Lorenz Bauer
2020-08-19 15:48   ` Jakub Kicinski
2020-08-19 18:50   ` Yonghong Song
2020-08-19 20:11   ` John Fastabend
2020-08-19  9:24 ` [PATCH bpf-next 3/6] bpf: sockmap: call sock_map_update_elem directly Lorenz Bauer
2020-08-19 19:15   ` Yonghong Song
2020-08-19 20:29   ` John Fastabend
2020-08-19  9:24 ` [PATCH bpf-next 4/6] bpf: override the meaning of ARG_PTR_TO_MAP_VALUE for sockmap and sockhash Lorenz Bauer
2020-08-19 20:13   ` Yonghong Song
2020-08-20 12:33     ` Lorenz Bauer
2020-08-19 20:51   ` John Fastabend
2020-08-19  9:24 ` [PATCH bpf-next 5/6] bpf: sockmap: allow update from BPF Lorenz Bauer
2020-08-19 20:35   ` Yonghong Song
2020-08-19 21:22   ` John Fastabend [this message]
2020-08-19 22:41     ` John Fastabend
2020-08-20 11:33       ` Lorenz Bauer
2020-08-20 14:45         ` Yonghong Song
2020-08-19  9:24 ` [PATCH bpf-next 6/6] selftests: bpf: test sockmap " Lorenz Bauer
2020-08-19 20:45   ` Yonghong Song
2020-08-20 11:58     ` Lorenz Bauer
2020-08-20 14:49       ` Yonghong Song
2020-08-20 16:12         ` Lorenz Bauer

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